1. Field of the Invention
This invention relates to a circuit breaker and, more specifically, to a shield structure which directs ionized gases, created by separation of the circuit breaker's contacts, away from a collar assembly coupled to the line side of a circuit breaker.
2. Description of the Prior Art
Molded case circuit breakers are generally known in the art. Such circuit breakers are used to protect electrical circuits from damage due to an overload, a short circuit or both. Circuit breakers typically have a molded plastic housing enclosing at least one pair of separable contacts including a fixed contact and a moveable contact. During an overload or a short circuit, the circuit breaker will trip causing the contacts to separate thereby opening the circuit. Additionally, the circuit breaker may be tripped manually should the need arise.
When the electrical contacts within a circuit breaker separate, an electrical arc may form between the contacts creating hot ionized gases. The ionized gases formed by an electrical arc are conductive. If these ionized gases collect in the vicinity of the line terminals of the circuit breaker, they may establish a conduction path between the terminals connected to different phases of the line current, or between the terminals and an electrical ground. Such a connection can lead to electrical faults on the line side of the circuit breaker and damage the equipment. Circuit breakers typically include vents to allow the ionized gases to quickly escape as well as a shield to protect a collar assembly which connects the line to the terminal strap or contact.
A collar assembly will generally have a four sided collar defining a cavity. The collar is attached to the terminal strap which incorporates the fixed contact of the circuit breaker. The collar will also have a screw, or other such device, which may be used to clamp the line end against the terminal strap. The collar and the line end are in close proximity to the contact point of the circuit breaker and, when the circuit is broken, ionized gases are in the immediate vicinity of the line end and collar assembly. To deflect the ionized gasses away from the collar assembly and towards a vent, most collar assemblies include a gas deflector.
Prior art gas deflection devices include a generally L-shaped paper shield mounted on top of the collar which overlays the contact side of the collar, as well as a separate plastic sleeve disposed about the screw and passing through the paper shield. This design has several disadvantages. For example, because the paper shield device is not coupled to the collar assembly, it can easily be accidentally removed. Also, because the paper shield is not fixed, it may move within the circuit breaker housing, allowing a path for ionized gases to reach the collar assembly and line. Because the screw sleeve is not integral to the paper shield, another path for ionized gases to contact the collar assembly could exist through the screw sleeve hole in the paper shield. Additionally, because the paper shield and screw sleeve are separate components, there is an additional cost associated with assembling the device.
There is a need for a gas deflection device to isolate the line end terminals of a circuit breaker from each other and areas adjacent to the circuit breaker to substantially reduce the amount of ionized gases infiltrating into those spaces.
There is a further need for a gas deflection device which is compatible with collar assemblies presently used on circuit breakers.
There is a further need for a gas deflection device which is inexpensive and may be conveniently installed within a circuit breaker.